This invention relates to a magnetically driven chemical pump having a two piece, separable impeller and inner drive.
Magnetic drive centrifugal pumps include a wet portion, which contains the process fluid that is being pumped, and a dry portion having a drive, which provides power to the pumped fluid. The dry portion is exposed only to the atmosphere surrounding the pump. In one typical magnetic drive design, an inner and outer drive are separated by a plastic containment shell, which prevents the pumped fluid from escaping to the environment. The outer drive, which is usually driven by an electric motor, is located in the dry portion and magnetically drives the inner drive in the wet portion that is attached to a pump impeller. Since magnetic drive pumps are seal-less, they are often selected to pump very acidic or caustic process fluids, such as hydrochloric acid, nitric acid, and sodium hypochlorite.
The inner drive, which includes magnets, and impeller are typically integrally formed with one another. A plastic coating surrounds the magnets preventing the magnets from corroding and the pump from failing. Typically, the impeller is constructed from a fiber reinforced plastic to provide strength, which dictates that the plastic encapsulating the magnets be formed from the same material. However, the reinforcing fibers permit the process fluid to wick into the area with the magnets thereby permitting corrosion. Accordingly, it is desirable to use a non-reinforced plastic to encapsulate the magnets.
Inner drive assemblies have been proposed that have an impeller that is separable from the inner drive. In one example arrangement, a pentagonal extension from the impeller is received in a corresponding shaped aperture in the inner drive to permit the transfer of torque from the inner drive to the impeller. The coupling between the impeller and the inner drive typically causes cold flowing of the plastic, which undesirably distorts the plastic coating.
The separable impeller and inner drive have been secured by various locking features. In one example, multiple pins are used to retain the impeller and inner drive. In another arrangement, flexible prongs are received by the inner drive. A bushing directly supports the locking feature provided by the impeller, but does not directly support the inner drive. Instead, the inner drive is supported by the impeller requiring the tolerances between the inner drive and impeller interface to be tightly maintained to provide desired alignment between the bushing and inner drive.
What is needed is an improved two piece, separable impeller and inner drive that addresses the problems described above.